(1) Field of the Invention
This invention relates to package scanning systems, in particular to scanning bar code from of the bottom-surface of packages being transported in a continuous motion along a conveyor.
(2) Background of the Invention
The use of barcode labels is a popular method for attaching machine-readable data to a wide variety of products and materials. Barcode scanners are used to interrogate the barcode labels and the data read from the label is used in a variety of identification, tracking, and control applications. When the scanner scans the bar code in a direction other than perpendicular to the bars of the labels, some of the bars may be missed during scanning. To cover a oblique bar code, the barcode label may be scanned multiple numbers of times line by line over an area of the bar code frame like the rasters of a television picture. Then the labels are less likely to be missed. For more versatility, the barcode may be scanned from light sources oriented from different directions. The readings from multiple passes are composed to xe2x80x9creconstructxe2x80x9d the correct code.
In many material-handling systems, barcode scanners are used to automatically interrogate packages or parcels as they are transported on a conveyor. In highly automated applications, multiple barcode scanners are used in what is called a xe2x80x9cscanning tunnelxe2x80x9d to simultaneously scan multiple sides of a package and thus accommodate a nearly random orientation of packages on the conveyor. Current technology has limited the effectiveness of the scanning tunnel applications to reading the top and sides of the packages only. Reading the bottom surfaces is problematic since the typical conveying mechanism blocks the optical view of the package from underneath the conveyor. Optical scanners sweep the reading area with a scanning laser or line scanning imaging camera. These systems need a full and unrestricted view of the reading area, i.e. the scanner must not miss a single bar of the barcode label. Any optical restriction across the viewing area which cause any bar to be missed by the scanner, no matter how small, causes error in the scanning process and make the scanning ineffective. When a package is transported on a conveyor, the surface on which the barcode is printed may appear on any one surface of the six sides of a rectangular box, which is randomly thrown on the conveyor belt. If the barcode happens to be printed on the underside, then the scanner is unable to read the bar code. Reading barcodes from underneath the conveying surface is further complicated by a random orientation of the barcode labels. Barcode reading technology requires that all elements of the printed barcode symbols be read by the optical sweep of the scanner laser. Different barcode labels have different aspect ratios for the height and width of the field of barcode symbols. A single barcode scanner can effectively read a given barcode label only within a specific tolerance to angular offset. Beyond this angular tolerance the geometry will not allow the scanning line to pass through all barcode symbols and reading the label data is not possible. Recent advances in software allow a certain amount of xe2x80x9creconstructionxe2x80x9d of the entire barcode data from multiple successive yet partial reads of the printed symbol array. This technique effectively increases the angular tolerance for the reading the barcode data. However there is still a practical limit to the degree of reconstruction and multiple scanning line orientations are needed to read randomly oriented barcodes.
More advanced Omni and Holographic style scanners emit a multitude of scanning lines at different orientations from the same scanner. This technique has a lower read rate since a single scanner will produce many scanning lines for the one orientation that is successful. However this technique greatly improves the probability of getting a successful read from a single scanner. Omni and Holographic scanners have been successfully used for reading the underside surface of packages, but not on a conveyor belt. A common application is in a grocery store check out line where an Omni-directional and/or holographic scanner is mounted underneath a glass plate where the clerk will push the product over. This solution is effective however the size of the viewing aperture required makes this technique difficult to integrate in a fully automatic conveyor system which will maintain high production rate of material transport. Another problem is the need for human handling, which is not cost effective.
The object of this invention is to read the bar code at the underside of a package being transported on a conveyor. Another object of this invention is to construct a conveyor capable of reading the bar code at the underside of the package. Still another object of this invention is to perform underside scanning of packages continuously in a steady flow on an automatic conveyor transport system. A further object of this invention is to provide an inexpensive and less labor intensive scanning system for reading the barcodes .
These objects are accomplished by designing a conveyor with several narrow and open apertures over which material is smoothly transported as if on a continuous surface. The multiple apertures are positioned at different angles to each other and each aperture provides a dedicated scanner to the bottom side of packages being transported on the conveying surface. The number of apertures and their angular position is determined, in part, by the aspect ratio of the barcodes that are to be processed. The multiple barcode scanners mounted at different angles collectively read the barcode on the underside of a transported package regardless of its orientation.
The invention presents an inexpensive technique to perform underside scanning of packages with convenient high speed linear scanners as they are transported in a steady flow on an automatic conveyor transport system.